Loudspeaker



- May 31, 1938'.' ENGHOLM 2,119,272

LOUDSPEAKER Filed July 5, 1934 @54 Baa-4, X/4Z vim Sum/wen Patented May31, 1938 c 1 q r UNi'iED STATES PATENT OFFIQE LOUDSPEAKER Bernard A.Engholm, Shaker Heights, Ohio, as-

signor to The Bola Company, Cleveland, Ohio, a corporation of OhioApplication July 5, 1934, Serial No. 733,757

2 Claims. (01. 179-4155) This invention relates to loud speakers, suchopening 13 into which the tip of the inner pole for exampleas those,which utilize a moving coil piece extends, whereby an annular air gap isthat operates in an air gap across a magnetic provided between the twopieces. A voice coil M field. Speakers, which have a magnetic field thatis removably mounted on a support !5, within is produced by a permanentmagnet usually comthe air gap, and the support in turn is attached prisea strip which is rectangular in cross secto a diaphragm l6, which isillustrated as being tion, and which has a width that is severaltimessubstantially conical in form. The interconnected the thickness. Thestrip is generally arranged in support and diaphragm are shown as beingatthe form of a U and supports an inner pole piece tached to a centeringmember I! which is rigidly on the intermediate portion, and an outerpole fastened at its inner periphery to the neck of 10 piece at the endsof the arms of the U. the diaphragm and at its outer periphery to theThe inner pole piece, heretofore, so far as I clampin rings The clampingrings n turn am aware, has been a solid cylinder, the diammay beattached to astationary diaphragm houseter of which has beenconsiderably smaller than ing 20, as by securing members 2 I.

it the width of the magnet. I have found however, I have found that ifthe inner pole piece is 15 that such construction is objectionable inthat made solid and of uniform diameter throughout it restricts theextent to which the magnet can its length,and that if the diameter isless than be charged at the time of excitation. I believe the width ofthe permanent magnet, that the that the restriction is due to the factthat the magnet can be charged, but that the extent of pole piece,because of its small size becomes satit will be materially less than ifthe inner pole 20 urated before the magnet, and thereby prohibits piecewere made in accordance with my inventhe introduction of suflicient fluxat the time of tion. The invention therefore, comprises a excitation tosaturate the magnet. As a result, structure in which the pole tip iscircular in crossthe flux distribution in the magnet does not havesection, within the regio 0f the a p ut is s the desired degree ofuniformity, and the density fla ed ward y om s region until it is isgreatly impaired. stantially equal to the width of the magnet.

An object of my invention therefore, is to make This is partic a lyShOWn in @6011- a low reluctance pole structure, which when apomy ofmanufacture, I make the inner pole piece plied to a permanent magnetenables it to be of laminations and fasten'them rigidly together,

39 charged to a much greater degree than any conas by rivets. structionheretofore designed, and of which I The permanent magnetic fieldstructure, which am aware. Furthermore, my invention is diis produced bymy invention, as described, greatrected to a construction which, whenthe magnet 1y increases the charge that can be imparted to is in usewill result in a field of greater intenthe magnet at the time ofexcitation, and prosity and of m r uniform fl x distribution, for ducesa structure that has more uniform flux a net of a given S e, d W ch ca emade distribution over any type of pole structure hereeconomically andreadily assembled. tofore used.

Referring now to the drawing, Fig. l'is a side I c1aim:- elevation,partly in section, of a loud speaker hav- 1 In a loud speaker having apermanent 40 mg Permenent field magnet; 2 is a real" netic structurecomprising a one-piece U-shaped 40 View O the peaker shown in Fig. 1,but on a striphaving substantially uniform width throughreduced Scale, wpa t Of e magnet broken out its length, and having an inner pole piecefasaway to show the interior construction, and Fig. tened thereto, theinner pole piece comprising a 3 is a sectional v taken through themagnet plurality of flat plates which extend parallel to to show theinner pole piece in side elevation. each other and in the same directionas the arms 45 The loud speaker with which I have illusof the U, andhaving an outer pole piece attrated my invention has a permanentmagnetic tached to the ends of the arms and having an field structure,which comprises a U-shaped opening that cooperates with the inner polepiece magnetic strip iii, towhich an inner pole piece to provide anannular air gap, one end portion mi N is rigidly connected, adjacent themidportion of the plates forming a cylinder and the interthereof, and towhich an outer pole piece I2 is mediate portion of the plates beingflared in connected at the ends thereof. Pole pieces are all planeswhich transversely cut the midportion preferably attached to the strip58 by welding, of the U-shaped strip. although other forms of connectionmay be uti- 2. A magnetic structure for a loud speaker lized, ifdesired. The outer pole piece has an comprising a permanent magnetic onepiece 55 nection thereto, the plates terminating at the opposite end ina reduced cylindrical tip which projects into the opening in the outerpole piece to provide an annular air gap.

BERNARD A. ENGHOLM.

